With electrochemical devices such as electric double layer capacitors, a very small amount of water in the electrolytic solution is reduced along with oxygen when voltage is applied to the device, generating OH− ions in the vicinity of the negative electrode. These OH− ions cause corrosion to the sealed opening portion of the negative electrode, entailing a solution leak and leading to the problem of lowering the reliability of the electrochemical device.
In the case where the cation is a quaternary ammonium salt, it is impossible to inhibit the formation of OH− ions, but it has been disclosed to effectively diminish the alkali produced by using an amidine electrolyte as means for solving such a problem (e.g., Patent Literatures 1 and 2).
According to Patent Literatures 1 and 2, electrolytic solutions comprising an amidine electrolyte are usable without giving rise to trouble such as solution leaks due to the degradation of sealing rubber during constant-voltage electrolysis unlike the quaternary ammonium salt conventionally used as an electrolyte, effectively reducing the amount of alkali. However, electrolytic solutions wherein an amidine electrolyte is used are generally lower in voltage resistance than quaternary ammonium salts and therefore have the problem of encountering difficulties in providing electrochemical devices of higher capacitance.
[Patent Literature 1] WO 95/15572
[Patent Literature 2] JP1996-321439A
An object of the present invention is to provide electrolytic solutions wherein formation of OH− ions is inhibited even in the event of electrochemical alteration to diminish the degradation or corrosion of resins, rubbers or metals and to give improved reliability to electrochemical devices, and to further provide electrochemical devices wherein the electrolytic solution is used.